System and method for spatial and spectral imaging

ABSTRACT

A system and method for acquiring images containing spatial and spectral information of an object include acquiring defocused images using an optical system based on extended depth of field. The optical system further includes a filter array comprising an array of at least six different sub-filters that are arranged such that any group of four immediately adjacent sub-filters includes at least one red sub-filter, at least one green sub-filter and at least one blue sub-filter. The filter array is located at the aperture stop of the optical system. A coded mask is located at the focal plane of the optical system, and an imager is located beyond the focal plane such that images acquired by the imager are defocused. The images are refocused, and spectral and spatial information is restored by designated software.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application claims the benefit of U.S. Provisional Application Ser.No. 61/588,787, filed Jan. 20, 2012, which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the field of imaging. In particular,the present invention relates to a system and method for acquiringimages of an object, while providing multi-band spectral information aswell as spatial information of the object.

BACKGROUND OF THE INVENTION

Imaging an object may be considered as a collection of points from theplane of the object that are being focused by an optical system onto acollection of points on the plane of an image sensor. When there is aneed to obtain spectral information as well as spatial information ofthe object, there is a fundamental problem, since this task isessentially the need to simultaneously capture a two-dimensional imageof the object plane together with the color of each point of the objectplane, this being essentially a “third dimension” of the object plane,and to record these three dimensions of information on thetwo-dimensional plane of the image sensor. A number of proposedsolutions have been suggested in the prior art to solve this problem.

One of the possible optical systems may be one that includes an array ofpinholes that may be positioned at the focal plane of the lightreflected off the object, while the image sensor is located beyond thefocal point such that the image acquired is defocused (and would belater focused by appropriate software). The pinhole array is used todifferentiate between points from the plane of the object, such thatthere won't be any overlap of points in the plane of the image sensor.Without the pinholes there is overlap between points on the imager'splane, which would make it practically impossible to correlate betweenpoints on the imager's plane to points on the object's plane and thuspractically impossible to restore the spatial information of the object.

A filter array comprising sub-filters may be added to the system and maybe positioned at the aperture stop, such that spectral information maybe acquired by the optical system as well as spatial information. Thatis, every pixel at the imager's plane has two “coordinates”; one for theangle at which light was reflected off the object, and a second for thesub-filter which the light reflected off the object passed through.However, the main disadvantages of using a pinhole array is losingspatial information, and losing light when collecting the lightreflected off the object, since the pinhole array blocks some of thelight reflected off the object from being projected onto the imager. Oneof the groups implementing such an optical system is, for example, theMITRE Corporation, Mclean, Va. (Horstmeyer R., Athale R. and Euliss G.(2009) “Modified light field architecture for reconfigurable multimodeimaging”. Proc. of SPIE, Vol. 7468, 746804).

Another possible optical system that may be used to create an image ofan object while providing spatial and spectral information is one whereinstead of a filter array located at the aperture stop, a mask islocated at the aperture stop. The mask, according to Wagadarikar et al.a group from Duke University, Durham, N.C., USA, is called a ‘codedaperture’ (A. A. Wagadarikar, N. P. Pitsianis, X. B. Sun and D. J. Brady(2009). “Video rate spectral imaging using a coded aperture snapshotspectral imager.” Optics Express 17(8): 6368-6388). The optical systemdescribed in this article does not comprise a pinhole array so there isan overlap between pixels of the image sensor. The mask is random withthe requirement of being 50% open for passage of light that is reflectedoff the imaged object. With this optical system there is minimal loss ofspatial resolution, since the scenes that are being imaged do notconsist of dramatic spectral changes, and the objects are relativelylarge so it is not difficult to distinguish between areas of the samespectra.

The mask, according to the above optical system, provides combinationsof spatial and spectral “coordinates” that may describe the object. (The“coordinates” are acquired by the imager followed by softwarereconstruction, in order to focus the acquired images). In areas of theobject where the spectrum is substantially similar, only the spatialdata is missing. The mask is then used to separate between close pointswith similar spectrum on the imager's plane, so it would be easier tocorrelate those points to points on the object's plane. However, whenclose points on the object have different spectrum (e.g., along theedges of the object) it is more difficult to distinguish between thepoints projected onto the imager.

Images that provide spatial as well as spectral information may beimportant within small scale in-vivo imaging devices, e.g., endoscopesand capsule endoscopes. Spatial information is needed in order todetermine the in-vivo location of the device, and spectral informationof in-vivo tissue is important for determining various diseases at earlystages that may be expressed in changes in spectra of various in-vivoparticles, e.g., hemoglobin. There is therefore a need for a new opticalsystem that may be implemented into devices that are to be insertedin-vivo, in order to acquire images that contain both spatial andspectral information.

SUMMARY OF THE INVENTION

In order to implement an optical system providing spatial and spectralinformation into in-vivo devices, a few changes should be made to theoptical systems described above.

According to some embodiments of the present invention, the opticalsystem is based on Extended Depth Of Field (EDOF) optical systems, inorder to substantially remove the dependency of the size of the spot oflight reflected off the object and projected onto the imager, andchanges in spectral mapping, on the distance between the object and theoptical system. Furthermore, in some embodiments of the presentinvention, the optical system may comprise a filter array with a specialarrangement of the sub-filters of the array. The arrangement of thesub-filters may be such that any group of four immediately adjacentsub-filters includes at least one red sub-filter, at least one greensub-filter and at least one blue sub-filter. The filter array istypically located at the aperture stop of the optical system of theinvention.

According to some embodiments, A system for acquiring images containingspatial and spectral information of an object may comprise an extendeddepth of field optical system, a filter array comprising an array of atleast six different sub-filters that may be arranged such that any groupof four immediately adjacent sub-filters comprises at least one redsub-filter, at least one green sub-filter and at least one bluesub-filter. The filter array may be located at the aperture stop of theoptical system. The optical system may further comprise a coded maskthat is located at the focal plane of the optical system, and an imagerthat may be located beyond the focal plane such that images acquired bythe imager are defocused.

In some embodiments, the filter array comprises nine differentsub-filters. In other embodiments, the filter array may comprise sixdifferent sub-filters, and three different sub-filters that each is aduplicate of one of the six different sub-filters.

In some embodiments, the sub-filters of the filter array may be selectedfrom wavelengths that correspond to absorption spectra of hemoglobin.The sub-filters may be selected from the following wavelengths: 420,470, 510, 540, 560, 570, 600, 620, 630, 660, 800, and 880 nm.

In some embodiments, the coded mask may be a random mask. According tosome embodiments, the coded mask may be between 40% to 60% transmissiveand, respectively, between 60% to 40% closed for passage of light. Forexample, in some embodiments, the coded mask may be 50% transmissive forpassage of light. Other random masks may be used. In some embodiments,the coded mask may comprise hyper-pixels arranged at groups of threeover three hyper-pixels. The coded mask may be arranged such that forany three over three hyper-pixels at least one hyper-pixel is open andat least one hyper-pixel is closed.

According to some embodiments, the focal plane of the system may belocated at the top end of the cover glass of the imager. The imager maybe a black and white imager.

In some embodiments, a capsule endoscope may comprise the optical systemdescribed above, while the location of the focal plane may be at the topend of the cover glass or inside the cover glass, and the coded mask maybe located at the top end of the cover glass.

According to some embodiments, a method for acquiring images containingspatial and spectral information of an object may comprise the steps of:acquiring defocused images using the system described above, refocusingthe acquired images, and restoring spatial and spectral information ofthe object according to the location of the imager's pixel thatcollected the light, and according to the wavelength of the lightcollected by the imager, respectively. In some embodiments, the step ofrefocusing of the images may be performed by designated software. Insome embodiments, the step of restoring spatial and spectral informationof the object may be performed by designated software, either the samesoftware that performs refocusing of the images or different software.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description taken in conjunction with theappended drawings in which:

FIG. 1 is a schematic illustration of a first optical system, inaccordance with the prior art;

FIG. 2 is a schematic illustration of a second optical system, inaccordance with the prior art;

FIG. 3 is a schematic illustration of an optical system based onextended depth of field for acquiring images containing both spatial andspectral information of an object, in accordance with embodiments of thepresent invention;

FIGS. 4A-4B are schematic illustrations of a focal plane located at thetop end of the cover glass and a focal plane located inside the coverglass, respectively, in accordance with embodiments of the presentinvention;

FIG. 5 is a schematic illustration of a filter array, in accordance withembodiments of the present invention;

FIGS. 6A-6B are schematic illustrations of two arrangements ofsub-filters of the filter array, in accordance with embodiments of thepresent invention; and

FIG. 7 is a flow chart describing a method for acquiring imagescontaining both spatial and spectral information of an object, inaccordance with embodiments of the present invention.

It will be appreciated that, for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn accuratelyor to scale. For example, the dimensions of some of the elements may beexaggerated relative to other elements for clarity, or several physicalcomponents may be included in one functional block or element. Further,where considered appropriate, reference numerals may be repeated amongthe figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, various aspects of the invention will bedescribed. For purposes of explanation, specific configurations anddetails are set forth in order to provide a thorough understanding ofthe invention. However, it will also be apparent to one skilled in theart that the invention may be practiced without the specific detailspresented herein. Furthermore, well-known features may be omitted orsimplified in order not to obscure the invention.

The system and method described with respect to embodiments of thepresent invention provide acquisition of images containing both spatialand spectral information of the imaged object.

Reference is now made to FIG. 1, which schematically illustrates a firstoptical system according to the prior art. Optical system 100 of theprior art comprises lens 102 and filter array 103, both of which arelocated at the aperture stop of the optical system 100. Optical system100 further comprises a pinhole array 104, which is located at the focalplane of optical system 100, and imager 105, which is located beyond thefocal plane of system 100, such that images acquired by imager 105 aredefocused. The defocused images may later be refocused using appropriatesoftware.

The pinhole array 104 is used to differentiate between points from theplane of the object 101, such that there isn't any overlap of points inthe plane of the imager 105. Without the pinhole array 104 there wouldbe overlap between points on the plane of imager 105, which would makeit practically impossible to correlate between points on the plane ofimager 105 to points on the plane of the object 101 and thus practicallyimpossible to create a substantially accurate image of the object.

Filter array 103 is composed from a plurality of sub-filters. Filterarray 103 is positioned at the aperture stop of optical system 100, suchthat spectral information may be acquired by optical system 100, as wellas spatial information. That is, every pixel at the plane of imager 105has two “coordinates”; one for the angle at which light was reflectedoff object 101, and a second for the sub-filter which the lightreflected off object 101 passed through. However, the main disadvantagesof using a pinhole array, e.g., pinhole array 104, is losing spatialinformation, and losing light when collecting the light reflected offthe object, e.g., object 101, since the pinhole array blocks some of thelight reflected off the object from being projected onto the imager,e.g., imager 105. Only part of the light reflected off the object passesthrough pinhole array 104, since only light that reaches the pinholes ofpinhole array 104 may in fact pass through pinhole array 104.

Reference is now made to FIG. 2, which schematically illustrates asecond optical system, in accordance with the prior art. Optical system200 comprises objective lens 202, coded aperture or coded mask 203 thatis located at the aperture stop, band-pass filter 204 (for limiting therange of wavelengths that would reach the imager 207), relay lenses 205,prism 206 (for providing a wide and continuous range of spectra) andimager 207. Optical system 200 does not comprise a pinhole array as doesoptical system 100, so typically there should be overlap between pointson the plane of the imager 207, which would make it difficult to restoretheir location on the plane of the object, e.g., object 201. However,optical system 200 comprises a mask 203. Mask 203 is a random mask,which is 50% open for transfer of light, that is, only 50% of the lightthat reaches mask 203, passes through it.

Every pixel at the plane of imager 207 has two “coordinates”; one forthe angle at which light was reflected off the object 201, and a secondfor the wavelength of the light reflected off object 201, which passedthrough prism 206. Optical system 200 is mainly useful when used toimage scenes that do not involve major changes in spectra throughout thescene. Therefore, mask 203 is used to differentiate between adjacentpoints on the plane of object 201, which have similar spectra, and whichdue to the mask, appear as different points on the plane of imager 207.However, when adjacent points on the plane of object 201 have differentspectra, it is more difficult to correlate between points on the planeof imager 207 to points on the plane of object 201, since in this caseboth the spatial and the spectral information are missing.

Reference is now made to FIG. 3, which schematically illustrates anoptical system according to embodiments of the present invention, whichenables acquisition of images of an object, which contain both spatialand spectral information of the object. As will be described in detailshereinbelow, the optical system according to embodiments of the presentinvention differs from the prior art in at least three major aspects.One difference is that the optical system may be based on Extended DepthOf Field (EDOF) optical system with the addition that the focal planemay be located at the top end of the cover glass of the imager, i.e., atthe end of the cover glass that is farthest from the imager (or it maybe located inside the cover glass) instead of on the imager, as inclassic EDOF systems. Another difference is that instead of using apinhole array, a mask may be used but at a different location thanproposed by the prior art. According to embodiments of the presentinvention, the mask may be located at the focal plane instead of at theaperture stop. And additional major difference is in the arrangement ofthe filter array located at the aperture stop. According to embodimentsof the present invention, the filter array may be arranged such that anycombination of four immediately adjacent sub-filters comprises at leastone sub-filter selected from the red spectra, which allows passage oflight of the selected red spectrum, at least one sub-filter selectedfrom the green spectra, which allows passage of light of the selectedgreen spectrum, and at least one sub-filter selected from the bluespectra, which allows passage of light of the selected blue spectrum. Insome embodiments, the sub-filters are selected from wavelengths thatcorrespond to the absorption spectra of hemoglobin; therefore, thefilter array may enable acquisition of an image of in-vivo tissuecontaining spectral information relevant to the pathological conditionof the tissue.

As shown in FIG. 3, optical system 300 may comprise objective lens 302,and filter array 303 for providing spectral information. The filterarray 303 may be located at the aperture stop of optical system 300.Filter array 303 may be composed of sub-filters, as will be described indetails with regards to FIG. 5. Optical system 300 may further comprisea set of field lenses 304, and imager 306 with cover glass 305 placed infront of it, between imager 306 and field lenses 304. The path of lightreflected off a certain point of object 301, and which passes throughoptical system 300 until it is projected onto imager 306 is depicted aslight rays 307. Light rays 307 are only one example of many other lightrays that may be reflected off other points of object 301.

Optical system 300 may be designed as Extended Depth Of Field (EDOF)optical system, with one change from classic EDOF systems. In classicEDOF optical systems the focal plane is on the imager, i.e., the imagesacquired by classic EDOF systems are focused. However, in optical system300 the focal plane is not on the imager 306 but rather on the top endof cover glass 305, i.e., on the end/side of the cover glass that isfarthest from imager 306. That is, images acquired by imager 306 aredefocused.

Defocusing of the images acquired by imager 306 is necessary in orderfor the images to contain both spatial and spectral information of theobject (e.g., object 301). If the images were to be focused at the planeof imager 306, any ray of light reflected off a certain point of object301, would eventually be focused onto substantially the same imager'spixel. This would make it practically impossible to determine throughwhich sub-filter (of filter array 303) the light ray passed, which meansit would be practically impossible to acquire spectral information. Byplacing imager 306 beyond the focal plane such that images acquired byimager 306 are defocused, the information on the angle of the reflectedlight may be determined, thus spectral information may be determined.

Furthermore, standard cameras are designed to acquire images frominfinity, whereas small scale devices, e.g., capsule endoscopes ortraditional endoscopes, need to acquire images from close distances. Inclose distances, the location of the focal plane changes withcorrelation to the distance between the imaged object and the opticalsystem (or between the object and the aperture stop, or between theobject and the imaging device comprising the optical system). If thelocation of the focal plane of the optical system changes, the spectralmapping is different for the same object positioned at differentdistances from the optical system. For different distances of the (same)object from the optical system, the light would be projected orcollected by different pixels of the imager, which would affect thespectral information collected by the imager and the size of the spot oflight projected onto the imager. Therefore, an EDOF optical arrangementwith defocusing at the plane of imager 306 may be used (e.g., in smallscale devices) so as to ensure that objects at substantially anydistance from imager 306 would be defocused at the same amount. As shownin FIG. 3, at the top end of cover glass 305, (which is the end of coverglass 305 farthest from imager 306), light rays 307 are not focused atone point but rather light rays 307 are focused along a distance priorto and at the top end of cover glass 305. That distance along whichlight may be focused at, may ensure that the size of the spot of lightprojected onto imager 306, as well as the spectral information stay thesame for substantially any distance between object 301 and opticalsystem 300. According to some embodiments, a coded mask may be locatedat the focal plane of optical system 300. According to FIG. 3, the focalplane is located at the top end of cover glass 305; therefore, a codedmask may be positioned at the top end of cover glass 305 of imager 306.

In some embodiments, the coded mask may be randomly selected. In otherembodiments, the coded mask may have several requirements other thanbeing completely random, e.g., that no pattern would be created by themask. In some embodiments, the mask may be between 40% to 60%transmissive for light reflected off an object to pass through it, andthus, respectively, between 60% to 40% closed to prevent light reflectedoff the object to pass through it. For example, the coded mask may be50% transmissive for passage of light. According to embodiments of theinvention, the coded mask may comprise hyper-pixels arranged at groupsof three-over-three hyper-pixels (which may correspond to a filter arraycomprising nine sub-filters, as will be described in details withregards to FIG. 5). Furthermore, the coded mask may be arranged suchthat for any combination of three-over-three hyper-pixels, at least onehyper-pixel is open and at least one hyper-pixel is closed.

The mask may be used to separate between points that are close to oneanother on the plane of the object. Assuming the imaged object hassubstantially uniform spectra, as common, for example, in thegastrointestinal (GI) tract, the main information that could beextracted from the image while using the mask, may be related to spatialinformation of the object. In the GI, for example, the main changeswithin an imaged scene are spatial changes, whereas the spectrum of thescene is substantially uniform. After light that is reflected off theobject passes through the mask and onto the imager, the acquired imagerequires reconstruction in order to determine the “real” image of theobject. The effect of the mask may be determined from images of scenesthat are substantially uniform both spatial and spectral wise. Accordingto the effect of the mask, several “solutions” of how the real image ofthe object is may be available. When implementing optical system 300within small scale in-vivo devices, e.g., devices that may be insertedinto the GI tract, various assumptions, e.g., assumptions related to GIscenes (such as that GI scenes are typically uniform spectral wise), maybe used in order to dilute the number of possible solutions.

Furthermore, when implementing optical systems, as optical system 300,into small scale in-vivo devices, few adjustments should be made. Forexample, the distance H (shown in FIG. 3) is defined as the distancebetween the aperture stop (e.g., aperture stop where filter array 303 islocated) and the focal plane (e.g., located at the end of cover glass305, which is the end farthest from imager 306). Distance h is definedas the distance between the focal plane (e.g., located at the end ofcover glass 305, which is the end farthest from imager 306) and theimager 306. These two distances h and H are relevant to the size of eachof the pixels of the imager (e.g., imager 306) and to the size of eachof the sub-filters of the filter array (e.g., filter array 303), asshown in the following equation:

$\begin{matrix}{\frac{{sub}_{filter} \cdot h}{H} \geq {pixel}} & (1)\end{matrix}$

In large scale devices, the ratio between h and H may be around 1:200,whereas, for example, h=1.5 mm, and H=300 mm. The same ratio should bemaintained in small scale devices, in order to acquire images of asimilar size as in large scale devices; however, the restriction of thesize of small scale devices should also be taken under consideration.Therefore, if H, which may be restricted, for example, by the size of alens assembly of a capsule endoscope, equals 2-3 mm, then h should beequal to 0.01-0.015 mm. The distance h between the focal plane and theimager is thereby very limited in size. One of the possible solutionsfor achieving such a small distance h may be by using a very thincoating on the imager's silicon chip, instead of using a cover glass.However, other solutions may be used.

Reference is now made to FIGS. 4A and 4B, which schematically illustratea focal plane located at the top end of the cover glass and a focalplane located inside the cover glass, respectively, in accordance withembodiments of the present invention. As shown in FIG. 4A, light rays307 are focused along a distance that begins at a point prior to the topend of cover glass 305, which is the end farthest from imager 306 andextends until the top end of cover glass 305. Light rays 307 are notfocused at one single point but instead are focused over a distance. Asdescribed above, this is mainly used in order to decrease the dependencyof the size of the spot (acquired by imager 306) on the distance betweenthe object and the optical system, e.g., optical system 300.

According to some embodiments, and as shown in FIG. 4B, light rays 307may be focused along a distance extending within the cover glass 305instead of at the top end of cover glass 305, which is the end farthestfrom imager 306 (as shown in FIG. 4A). Once again, this feature is usedin order to eliminate the dependency of the size of the spot on thedistance of the imaged object from the optical system, e.g. opticalsystem 300. Either of these two different possible locations of thefocal plane of an optical system based on EDOF (e.g. optical system300), may be implemented into in-vivo devices, e.g., capsule endoscopesor traditional endoscopes.

Reference is now made to FIG. 5, which schematically illustrates afilter array, in accordance with embodiments of the present invention.According to some embodiments, the filter array 303 (of optical system300) may comprise at least six sub-filters, and in the example shown inFIG. 5, nine sub-filters. The at least six sub-filters may be differentfrom one another, i.e., each of the sub-filters may allow passage oflight of a different narrow band wavelength from the rest of thesub-filters.

The sub-filters may be arranged such that any combination of fourimmediately adjacent sub-filters comprises at least one sub-filterselected from the red spectra, which allows passage of light of theselected red spectrum, at least one sub-filter selected from the greenspectra, which allows passage of light of the selected green spectrum,and at least one sub-filter selected from the blue spectra, which allowspassage of light of the selected blue spectra. The term “immediatelyadjacent”, specifically regarding four immediately adjacent sub-filters,means that each of the sub-filters directly contacts, at least at one ofits corners, every other one of the group of four sub-filters. Forexample, as shown in FIG. 5, the combination of R1-G2-B2-R2 comprises atleast one red sub-filter, at least one green sub-filter, and at leastone blue sub-filter. Another combination shown in FIG. 5 is R2-G2-B3-R3,which also comprises at least one red, at least one green, and at leastone blue sub-filter.

According to some embodiments, when filter array 303 comprises ninesub-filters, the nine sub-filters may comprise nine differentsub-filters, such that each sub-filter is selected from a differentwavelength of either the red, green or blue spectra. According toanother embodiment, the nine sub-filters may comprise six differentsub-filters (selected from either the red, green or blue spectra), whilethe last three are sub-filters already present among the six differentsub-filters. However, the three duplicate sub-filters may comprise atleast one sub-filter that corresponds to a wavelength selected from thered spectra, at least one sub-filter that corresponds to a wavelengthselected from the green spectra, and at least one sub-filter thatcorresponds to a wavelength selected from the blue spectra, all of whichare already present among the six different sub-filters initiallyselected.

According to some embodiments, in order to implement optical systems assystem 300 in-vivo, the sub-filters of the filter array may be selectedfrom wavelengths that correspond to the absorption spectra ofhemoglobin. Absorption spectra of hemoglobin may typically provideinformation on pathological condition of an in-vivo tissue. In someembodiments, the sub-filters may be selected from the followingwavelengths: 420, 470, 510, 540, 560, 570, 600, 620, 630, 660, 800, and880 nm. In other embodiments, other wavelengths may be selected. Inother embodiments, the sub-filters may be selected from wavelengths thatcorrespond to absorption spectra of other in-vivo components, e.g.,various biomarkers that may indicate on a biological state of thetissue.

Reference is now made to FIGS. 6A and 6B, which schematically illustratetwo possible arrangements of sub-filters of the filter array, inaccordance with embodiments of the present invention. FIGS. 6A and 6Bboth illustrate arrangements of sub-filters such that any fourimmediately adjacent sub-filters comprise at least one sub-filterselected from the red spectra, at least one sub-filter selected from thegreen spectra, and at least one sub-filter selected from the bluespectra. According to some embodiments, each of the nine sub-filters isof a different wavelength than the rest of the sub-filters.

The wavelengths of the sub-filters of filter array 303 according to FIG.6A may be as follows: λ1=420 nm, λ2=470 nm, λ3=510 nm, λ4=540 nm, λ5=560nm, λ6=570 nm, λ7=600 nm, λ8=620 nm and λ9=630 nm. Other arrangementsand other wavelengths may be used. The wavelengths of the sub-filters offilter array 303 according to FIG. 6B may be as follows: λ1=420 nm,λ2=470 nm, λ3=540 nm, λ4=570 nm, λ5=600 nm, λ6=620 nm, λ7=660 nm, λ8=800nm and λ9=880 nm. Other arrangements and other wavelengths may be used.

Reference is now made to FIG. 7, which illustrates a flow chartdescribing a method for acquiring images containing both spatial andspectral information of an object, in accordance with embodiments of thepresent invention. According to some embodiments, the method maycomprise the steps of: acquiring defocused images using an opticalsystem similar to optical system 300 (710), refocusing the acquiredimages (720), and restoring spatial and spectral information of theimaged object (730), according to the location of the imager's pixelthat collected the light, and according to the wavelength of the lightcollected by the imager, respectively. The sub-filter through whichlight passes through may determine the wavelengths collected by thepixels of the imager (e.g., imager 306). The location of the pixel alongthe imager that collected the light may be used to determine the spatiallocation along the object from which the light was reflected off.

In some embodiments, the step of refocusing the acquired images may beperformed by designated software. Refocusing of the acquired images maybe done by deconvolution, according to the appropriate point spreadfunction (which translates a point in the plane of the object to a pointin the plane of the imager). In some embodiments, the step of restoringspatial and spectral information of the imaged object may be performedby designated software. In some embodiments, the designated softwareused for restoring spatial and spectral information may be differentthan the software used to perform refocusing of the images. In otherembodiments, the software for restoring spatial and spectral informationmay be the same software used for refocusing the acquired images.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those of ordinary skill in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the invention.

1. A system for acquiring images containing spatial and spectralinformation of an object, the system comprising: an extended depth offield optical system; a filter array comprising an array of at least sixdifferent sub-filters, wherein said at least six sub-filters arearranged such that any group of four immediately adjacent sub-filterscomprises at least one red sub-filter, at least one green sub-filter andat least one blue sub-filter, and wherein said filter array is locatedat the aperture stop of said optical system; a coded mask located at thefocal plane of said optical system; and an imager located beyond thefocal plane such that images acquired by the imager are defocused. 2.The system according to claim 1, wherein said filter array comprisesnine different sub-filters.
 3. The system according to claim 2, whereinsaid filter array comprises six different sub-filters, and threedifferent sub-filters that each is a duplicate of one of the sixdifferent sub-filters.
 4. The system according to claim 1, wherein saidsub-filters of said filter array are selected from wavelengths thatcorrespond to absorption spectra of hemoglobin.
 5. The system accordingto claim 4, wherein said sub-filters are selected from the followingwavelengths: 420, 470, 510, 540, 560, 570, 600, 620, 630, 660, 800, and880 nm.
 6. The system according to claim 1, wherein said coded mask is arandom mask.
 7. The system according to claim 6, wherein said coded maskis 40%-60% transmissive and, respectively, 60%-40% closed for passage oflight.
 8. The system according to claim 6, wherein said coded mask is50% transmissive for passage of light.
 9. The system according to claim1, wherein said coded mask comprises hyper-pixels arranged at groups ofthree over three hyper-pixels.
 10. The system according to claim 9,wherein said coded mask is arranged such for any three over threehyper-pixels at least one hyper-pixel is open and at least onehyper-pixel is closed.
 11. The system according to claim 1, wherein saidfocal plane is located at the top end of the cover glass of the imager.12. The system according to claim 1, wherein said imager is a black andwhite imager.
 13. A capsule endoscope comprising the system according toclaim 1, wherein the location of said focal plane is at the top end ofthe cover glass or inside the cover glass, and wherein said coded maskis located at the top end of the cover glass.
 14. A method for acquiringimages containing spatial and spectral information of an object, themethod comprising: acquiring defocused images using the system accordingto claim 1; refocusing said acquired images; and restoring spatial andspectral information of the object according to the location of theimager's pixel that collected the light, and according to the wavelengthof the light collected by the imager, respectively.
 15. The methodaccording to claim 14, wherein refocusing of the images is performed bydesignated software.
 16. The method according to claim 14, whereinrestoring spatial and spectral information of the object is performed bydesignated software.